Hello Jon,
Thank you for reaching out.
Restore the Pro 6.7.3 site from the backup taken before the Slider Revolution update – This returns the site to Slider Revolution 6.7.37 and gets it working again. Slider Revolution 7 support was introduced in Pro 6.8.3 (Classic Revolution Slider element), with further fixes in Pro 6.8.4 (masthead display) and Pro 6.8.6 (deprecated method call). Pro 6.7.3 predates all of these, so 7.2.4 is not compatible with it. The correct update order is: backup, update Pro to 6.9.7, then install Slider Revolution 7.2.4 from Pro > Validation. Please apply the same order to the Pro 6.8.4 site, as 6.8.4 is also missing the 6.8.6 fix.
Regarding a 6.7.x fallback – The Validation screen distributes only the currently validated release, which is Slider Revolution 7.2.4. Previous Slider Revolution builds are not available for download from the Themeco Dashboard, so your pre-update backup is the fallback. Once Pro is on 6.9.7, the 7.2.4 install is the supported path forward.
PHP version for staging – Our Version Compatibility page currently lists PHP 7.4+ as supported and 8.0+ as recommended; PHP 8.4 is not yet listed. For your staging test, please target PHP 8.2 or 8.3 with Pro 6.9.7 and Cornerstone 7.9.7 installed first. If you choose to trial PHP 8.4, please enable WP_DEBUG_LOG and send us any deprecation or fatal entries so our developers can review them.
Kindly let us know how it goes.